Large-Scale Identification and Characterization of Heterodera avenae Putative Effectors Suppressing or Inducing Cell Death in Nicotiana benthamiana.

Changlong Chen,Yongpan Chen,Lingling Pan,Yiran Dai,Qian Liu,Fengwei Shi,Dan Yang,Heng Jian,Shanshan Yang

doi:10.3389/fpls.2017.02062

Abstract

Heterodera avenae is one of the most important plant pathogens and causes vast losses in cereal crops. As a sedentary endoparasitic nematode, H. avenae secretes effectors that modify plant defenses and promote its biotrophic infection of its hosts. However, the number of effectors involved in the interaction between H. avenae and host defenses remains unclear. Here, we report the identification of putative effectors in H. avenae that regulate plant defenses on a large scale. Our results showed that 78 of the 95 putative effectors suppressed programmed cell death (PCD) triggered by BAX and that 7 of the putative effectors themselves caused cell death in Nicotiana benthamiana. Among the cell-death-inducing effectors, three were found to be dependent on their specific domains to trigger cell death and to be expressed in esophageal gland cells by in situ hybridization. Ten candidate effectors that suppressed BAX-triggered PCD also suppressed PCD triggered by the elicitor PsojNIP and at least one R-protein/cognate effector pair, suggesting that they are active in suppressing both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). Notably, with the exception of isotig16060, these putative effectors could also suppress PCD triggered by cell-death-inducing effectors from H. avenae, indicating that those effectors may cooperate to promote nematode parasitism. Collectively, our results indicate that the majority of the tested effectors of H. avenae may play important roles in suppressing cell death induced by different elicitors in N. benthamiana.

Highlights

Heterodera avenae, the most commonly reported species of cereal cyst nematode (CCN), causes substantial crop yield losses of 30–100% in wheat production worldwide (Bonfil et al, 2004; Nicol et al, 2007)
The results showed that, of the 95 candidate effector genes evaluated, 78 genes (82.1%) suppressed BT-programmed cell death (PCD) to variable degrees; 10 genes (10.5%) had no obvious effect on BAX-triggered programmed cell death (BT-PCD), and 7 genes (7.4%) induced cell death or chlorosis in N. benthamiana leaves (Figures 1A,B)
We found that 78 putative effectors suppressed PCD triggered by BAX and 7 putative effectors induced cell death or chlorosis in N. benthamiana (Figure 1A and Supplementary Table S2)

Summary

Introduction

Heterodera avenae, the most commonly reported species of cereal cyst nematode (CCN), causes substantial crop yield losses of 30–100% in wheat production worldwide (Bonfil et al, 2004; Nicol et al, 2007). Plants respond to infection using two modes of innate immunity (Jones and Dangl, 2006; Tsuda and Katagiri, 2010). The first mode of immunity is referred to as “pattern-triggered immunity” (PTI) and is triggered by microbe-associated or pathogen-associated molecular patterns (MAMPs or PAMPs). Through evolution, adapted pathogens secrete effector proteins into plant cells and suppress PTI (Boller and He, 2009). Plants have evolved resistance (R) proteins that recognize certain pathogen effectors, resulting in initiation of the second mode of plant immunity, which is referred to as “effector-triggered immunity” (ETI) (Chisholm et al, 2006). The dynamic co-evolution of plants and pathogens is ongoing, and some pathogens have acquired effectors that interfere with ETI (Jones and Dangl, 2006). Plants and microbial pathogens are engaged in an endless “arms race.”

Methods

Results

Conclusion